Sweep collapse and rotation failure alarm system for ppi display device



Jan. 5, 1965 A. sHULMAN 3,164,745

swEEP COLLAPSE AND RoTATIoN FAILURE ALARM SYSTEM FoP. PPI DISPLAY DEVICE Filed May 2, 1961 2 sheets-sheet 1 Jan. 5, 1965 A, SHULMAN 3,164,745

SWEEP COLLAPSE AND ROTATION FAILURE ALARM SYSTEM FOR PPI DISPLAY DEVICE Filed May 2. 1961 2 Sheets-Sheet 2 mou Sitio J1 w92.. mam 9:. om M H mism 35u55 Qz Guam R M N 0 M L U L .n N A An; TI! ummm lIIL I m H .r 0 mou m Guam x SENSE Ritz@ 3E. B Umm w om .wam A 1 1 w3 E mmsm x v. om B E Q 2; LI

v5o. goo. .rl mmm mmm mmm United States Patentiiice This invention relates to a sweep collapse alarm systern and more particularly to a system for protecting electron tubes such as cathode-ray tubes or the like against destructive electron beam current.

In a PPI radar system several cathode-ray tubes are generally used as display devices.v If the sweep waveforms fail or the sweeping systems cease to rotate the Y rays will come to rest upon the fluorescent screens. If the rays remain stationary for even a very short period of time the fluorescent screens may be burned, rendering the cathode-ray tubes unfit as display devices. It is apparent that some means should be provided to protect the cathode-ray tubes against destructive beam current.

In connection with PPI displays, it is frequently desirable to include computed information corresponding to the predicted positions of various objects. The cornputed information may be distinguished by generating an additional scan waveform that produces a partial circle, a full circle, an ellipse or the like on the cathode ray tube screen, or increasing spot brillance during part or all of the additional scan. This additional waveform is commonly referred to as a tag waveform. The tag waveform may render ordinary protective circuits inoperative when the radar sweep waveform has collapsed; therefore, circuit means must be provided to separate the tag waveform from the radar waveform.

In a protection system it is often desirable to provide audio and visual indications of failure of the operation of the system and to provide means that will automatically reset the system after a given period of time to check whether or not the malfunction has been corrected. A manual reset switch and means to test the operation of the protection circuits are also desirable.

An object of my invention is to protect cathode-ray tubes in the event the sweep waveforms fail or cease to rotate the sweep on the cathode-ray tube screens.

Another object of my invention is to protect cathoderay tubes in the event the cathode-ray beam ceases to rotate unaccompanied by a sweep collapse.

Another object of my invention is to provide a novel cathode-ray tube protection circuit including audio and visual indications of a sweep malfunction.

Another object of my invention is to provide a novel cathode-ray tube protection system including automatic and manual reset means.

A still further object of my invention is to provide means to test the operation of a novel cathode-ray tube protection system. Y

The above mentioned and other objects of the invention will be apparent from the following description and accompanying drawings, in which like parts inthe various figures have like numerals and in which:

FIG. 1 shows a block diagram of a part of a PPI radar system including a novel protection system.

FIGS. 2A and B are schematic diagrams of a preferred embodiment of the invention.

FIG. 3 shows waveforms present at various points in the circuits of FIG. 2.

Referring to FIG. 1 of the drawings, two separate channels, channels A and B, having identical elements, are shown for the X-sWeep waveform and the Y-sweep waveform respectively. Since channels A and B are identical, the operation of only one of these channels will Patented Jan. 5, 1965 be described. Channel C, which includes amplifier 5, paraphase amplifier 6, and bridge clamp 7, is common to both channels A and B. lIn FIG. 1, the incoming X-axis sweep and tag waveform are fed through a resistance gate comprising cathode follower 1A for driving the sweep and tag Waveform andV amplifier 5, paraphase amplifier 6, and bridge clamp 7 for driving a sweep gate waveform. The sweep gate waveform gates out any waveform, including the tags, except the radar sweep waveform. The resultant waveform comprising only a resolved radar sweep waveform is applied to peak detector 3A through cathode-follower 2A. The peak detector generates a D.C. voltage that fiuctuates in synchronism with the antenna scan. This D.-C. voltage is applied to R.M.S. computer 9 through cathode follower 4A. A similar D.-C. voltage is applied to R.M.S. computer 9 from channel B. Theoretically, the output of the R.M.S. computer will be constant since one of the D.C. voltages fluctuates in accordance with the sine of the antenna azimuth angle while the other iiuctuates in accordance with the cosine of the antenna azimuth angle. The output of computer 9 saturates amplifier 10 and the output of amplifier 10 renders relay driver 11, non-conductive; thereby maintaining the protection circuits in the non-alarm condition.

On the other hand, if one or both of the sweep waveforms from channels A and B fail, then during at least a part of the antenna scan there will be no D.C. voltage presentv at the input of amplifier 10. During this period of zero output from computer 9, amplifier 10 will be cut-off.

`When amplifier 10 is cut-off, driver 11 is rendered conductive, thus actuating alarm relay K1 into the alarm position. Relay K1 is a multiple-contact relay, and when `it is actuated alarm light 13 turns on, alarm bell 14 rings,

and cathode-,ray tubes 17A-D are blanked. The cathoderays are removed from the screens of the tubes by means of blanking circuits 16A-D.

The invention as thus described cannot sense a cessation of rotation of the sweep unaccompanied by a sweep collapse, because in the absence of sweep rotation the voltages fed'into Vcomputer 9 will still be present, although not fluctuating. Some means must be provided to sense this cessation of rotation, for the screens of the cathode-ray tubes may be damaged if the scanning beam does not rotate. Rotation monitor 8 is provided to sense this rotation failure. Monitor 8 mixes the X and Y-sweeps fromfchannels A and B to obtain a D.C. voltage accompanied by a ripple having a frequencypfour times that of the antenna scan rate. If rotation of the sweep stops, a negative potential is applied to amplifier 10. This negative voltage is not suiiicient to cut-0H amplifier 10, but the output of thisl amplifier is reduced s'ufciently to allow relay driver 11 to conduct, thereby actuating alarm relay K1.y Thus, if no signal appears at the output of either monitor 8 or computer 9, driver 11 will conduct, and the protection circuits will assumeV the alarm condition in -the manner described above with reference to` a signal the malfunction has been corrected by this time, the radaris again ready to operate. If, however, the malfunction still exists, the alarm relay will again lock for a period of time somewhat shorter than 30 seconds,y after which the thermal time-delay relay will again release the alarm relay. This process continues repeatedly, so that a malfunction which is allowed to continue indefinitely, will 3 cause blanking accompanied by regular checks to see if the malfunction has been corrected.

Another feature of this invention is a provision to test the operation of the protective circuits. The operator can at any time, by energizing relay K3, check to see if the protection system is functioning properly.

A more detailed understanding of the operation of the protection system can be obtained by referring to FIGS. 2A and 2B which are schematic diagrams of the protective system. The sweep-gate Waveform applied to channel C is negative-going during the time the sweep is present in channels A and B. This negative-going pulse is fed to the grid of amplifier 5. The amplified sweepgate is taken from load resistor R82 and applied to the grid of paraphase amplifier 6. The signal developed across plate resistor RRS is negative while the signal developed across cathode resistor R86 is positive and the two signals are of equal amplitude. The negative-going signal from the plate of amplifier 6 back-biases diodes D12, D13, and D14. The positive-going signal from the cathode of amplifier 6 back-biases D15, D16, and D17. Diodes D12 through D17 are connected together to form bridge clamp 7. Bridge clamp 7 removes the tag voltages from the X and Y sweeps. The channel A, or X, output of bridge clamp 7 is connected to the junction of resistors R12 and R15. When the sweep gate is negativegoing the output of amplifier 6 keeps the junction between resistors R12 and R15 above ground so that the sweep voltage can be developed across resistor R13. During the tag time in channels A and B the input to channel C is zero volts and bridge clamp 7 clamps the junction between resistors R12 and R15 to ground. Thus, the only signal that is applied to the grid of amplifier 2A is the sweep signal because at all other times the output of amplifier 1A is shunted to ground by clamp 7.

f The sweep output of amplifier 1A is applied to the grid of amplifier 2A through a low-pass filter consisting of capacitor C1 and resistor R15. The low-pass filter removes any spikes or noise that may have been introduced by clamp 7. The output from amplifier 2A is applied through capacitor C2 to a clamping circuit consisting of diodes D and D21. This clamping circuit clamps the most negative portion of the sweep waveform to ground. Thus, when the sweeps are positive-going, the intervals between sweeps are clamped at ground, and when the sweeps are negative-going, the peaks of the sweeps are clamped at ground in a positive direction. This waveform is shown in E of PEG. 3. This ground-clamped waveform is applied to a peak detector consisting of diode 18, diode 19, capacitor C3 and resistor R19. As the sweep voltage goes positive, it passes through diodes 18 and 19 and charges capacitor C3. When the sweep returns to ground diodes 18 and 19 are back-biased, and C3 remains charged to almost the peak potential of the sweep because it can discharge only through resistor R19 which has a high resistance. If the peaks of Successive sweeps are higher the charge on capacitor C3 will increase with each sweep, provided the sweep voltage exceeds the voltage across the capacitor. Conversely, the time constant of capacitor C3 and resistor R19 is such that capacitor C3 will diS charge to follow the peaks of the sweep voltages if they become successively less positive. Thus, the output of peak detector 3A is the envelope of the waveform E in FIG. 3. Waveform C of FIG. 3 is the detected X-sweep and waveform D is the detected Y-swecp. That is, waveforms C and D are the detected waveforms when waveforms such as waveforms A and B of FIG. 3 are applied to channels A and B respectively. The waveforms A and B of FIG. 3 are the X and Y sweep waveforms modulated by the antenna rotation.

The detected waveform from detector 3A is applied to the grid of amplifier 4A and the output of this amplifier is applied to RMS. computer 9 and rotation monitor 8 (FIG. 2B). The output from amplifier 4B is also applied to both the R.M.S. computer and the rotation monitor.

R.M.S. computer 9 comprises diodes D1 through D4, resistors R23 through R30, and resistors R51 through R55. RMS. computer 9 performs an approximate rootmeans square computation. The degree phase-shift between the detected X and Y-sweeps prevents zero output from computer 9 if both linputs are present. In fact, the output of computer 9 is almost a constant voltage. Diodes 1 and 2 control the computation when the detected X-sweep is above the level of the detected Y-sweep and diodes 3 and 4 control the computationwhen the detected Y-sweep is above the level of the detected X-sweep. The output of the computer is coupled through resistors R55 and R56 to the grid of inverter amplifier 10. As long as both the X and Y-sweep voltages are present the positive voltage from computer 9 will hold amplifier 19 in a conducting state. If one or both of the sweep voltages fail, then during at least a part of the antenna scan, the output from computer 9 will be zero. At this instant amplifier 10 is cut-off by the bias voltage set by alarm adjust potentiometer RSS. The bias voltage is set at a level that will cut-off amplier 1t) when it is the only voltage present. When amplier lil is conducting, its plate voltage is about +30 volts. This positive 30 volts is not suflicient to overcome the -50 volts bias applied by voltage divider resistors R32 and R74 to the grid of driver amplier 11, and amplier 11 is therefore held non-conductive. However, when amplifier 10 is cut-off, the plate voltage rises and causes driver 11 to conduct. Conduction of driver 11 energizes alarm relay K1.

The detected X and Y-sweeps are also applied to rotation monitor 8 through capacitors C4 and C15, respectively. With constant rotation, the voltages varying at capacitors C4 and C15 are passed to rotation monitor diodes S through 11. Since the input to monitor 8 is always positive, the output will always be positive also. This positive voltage is blocked from the grid of amplifier 19 by diode 5 and the amplifier continues to conduct due to the output from computer 9. lf rotation stops, a negative potential developed at the junction of resistors R47 and R48 is coupled to the grid of amplifier 113` through diode 5. This negative potential does not cut-off amplier 1t), but reduces conduction sufficiently to allow arnplifier 11 to conduct and actuate alarm relay K1. From the foregoing remarks it is apparent that alarm relay K1 will be actuated if either or both ofV the sweeps collapse, or if the sweeps fail to .rotate in the absence of a sweep collapse. Y

When relay K1 `is actuated thevcathode-ray tubes are blanked by the application of a high negative voltage to blanking circuits 16 through contact arm 43 and resistor 50. Alarm lightr13, alarm bell 14, and reset means 15 are also placed in operation. -Contact arms 46 and 47 connect these circuits to-battery 41. Battery d1 ener gizes heater 44 of relay .42. This heat causes thermal contacts 43 to open after a period of time determined by the heating time of bimetallic contacts 43. Contact 49 of relay K1 connects the junction of resistors R32, R75, and R74 to ground through contacts 43 of relay 42 when relay K1 is energized. This effectively short-circuits the bias through R74 to ground so that amplifier 11 will con- ,tinue to conduct as long as contacts 43 and switch 45' remain closed. Switch 45 is normally closed and can be operated manually to momentarily open` the circuit when desired. Thus, thermal relay 42 operates as an automatic 4reset meansand switch 45 operates as a manual reset means. j

As was previously mentioned, it may be desirable to provide means to test the protection circuits. The testing is accomplished by energizing relay K3 with a locally generated signal. Energizing relay K3 transfers contactarm 32 from contact 3i) to contact 31. During the time that arm 32 is switching from one contact to the other, it is momentarily ungrounded. When arm 32 is ungrounded, the potential at the arm is determined by resistors R39, R90, and R91. Consequently, a pulse of appreciabie ane-'ams amplitude is applied by means of resistor R92 and diodes 6 and 7 to the grid of amplifier 1li. This pulse cuts-off amplifier llt), thereby causing the protection circuits to assume the alarm condition.

While the fundamental features of the invention as applied to a preferred embodiment have been shown and described in detail, it will be understood that various omissions, substitutions and changes in form and vdetails of the device illustrated, and in its operation, may be made by those skilled in the art, without departing from the spirit of the invention. It is the intention to be limited only as indicated by the scope of the following claims.

What is claimed is:

1. In a PPI radar system, a sweep collapse alarm system comprising: a rotation monitor; an RMS. computer; means to apply two input signals to |both said monitor and said computer, an amplifier coupled to said monitor and said computer; a relay driver coupled to said amplifier; and `a relay coupled to said driver.

2. In a PPI radar system, a sweep collapsev alarm system comprising: means to derive a firstsweep signal; means to derive a second sweep signal; first means for monitoring uctuations of the sweep signals; second means for monitoring the presence of sweep signals; means to apply said first sweep signal to said first and second monitoring means; means to apply said second sweep signal to said first and second monitoringmeans; an amplifier coupled to said first `and second monitoring means; a driver coupled to said amplifier; a relay coupled to said driver; and alarm means coupled to said relay.

3. In a 'PPI radar system, a sweep collapse alarm system comprising: a rotation monitoring means; computer means for determining the presence of sweep signals; means to `apply X- and Y-sweep input signals to both said computer means `and said monitor means; an ampli-fier coupled to said monitor means and said computer means; a relay driver coupled to said amplifier; a relay having at least one pair of contacts coupled to said driver; and cathode-ray tu'be blanking circuits coupled to said contacts.

put of said first and second channels and `an output; computer means for producing a signal wien the sweep voltages are present, said computer. means having an input coupled to the output of said first and second channels and having an output; an inverter amplifier connected in cornrnon to the output of said monitoring means and to the output of said computer means; a relay driver tube connected to the output of said amplifier; an alarm relay connected to the output of said driver tube; a plurality of blanking circuits coupled to said relai and a cathode-ray tube connected to each one of said blank circuits.

9. A protection system as described in claim 8 wherein a first input signal having a sweep waveform component and a tag waveform component is applied to said first channel and a second input signal having a sweep waveform component and a tag Waveform component is applied to said second signal channel; and wherein a third signal channel isycoupled to said first and second signal channels and includes means .to separate the tag Waveform from their respective sweep waveforms.

l0. A protection system as described in claim 8 wherein said first and second signal channels each include a first cathode-follower coupled tothe input, a second cathodei follower coupled to said first cathode-follower; .aj-peak detector coupled to said second cathode-follower, and a fourth cathode-follower having an input coupled to said peak detector` and an output coupled to both said monitoring means and said computer means and :wherein said third v signal channel comprises an amplifier having an input for terminals and the other connected to the other of said pair of output terminals and two outputs, one output connected ,beween said rst .and .second cathode follower of said first channel and the other outputy connected between said first and second cathode-follower of said second channel.

.-ll. A sweep collapse alarm system comprising: first input :signal means for vx-axis sweep signals; second input 4. In a PPI radar system, a sweep collapse alarm system comprising: a rotation monitoring means; a computer means; means to apply X- and Y-sweep input` signals t0 'both said monitor means and said computer means; an inverter amplifier coupled to the outputs of said monitor means and said computer means; a relay driver tube connected to said amplifier; a relay connected to said driver tube, said relay comprising a first pair of contacts, a second pair of contacts, a third pair of contacts4 and a fourth pair of contacts; automatic reset means connected to said first pair of contacts; a manual reset switch connected to said first pair of contacts; a plurality .of blanking circuits connected to said second pair of contacts; an audioindicator connected to said third pair of contacts;`an alarm light connected to said fourth pair of contacts; and a cathode-ray tube coupled to each one of said plurality of blanking circuits.

5. A sweep collapse alarm system as described in claim 4 wherein said automatic 4reset means comprises a thermal time delay relay having contacts controlling the bias on said relay driver tube. Y

6. A sweep collapse alarm system as described in claim 4 wherein means to test the operation of said alarm system by providing a test signal is connected to said arnplifier.

7. A sweep collapse alarm system as described in claim 6 wherein said test means comprises a voltage divider network and a relay having contacts connected to said divider network, to the input of said amplifier, and to ground.

8. In a PPI radar system, a cathode-ray tube protection system comprising: a first and a second signal channel `for X- and Y-sweep voltages, respectively, and each havingV an input and an output; means for monitoring the cathoderay sweep voltages to determine rotation of the sweep scan,

said monitoring means having an input coupled to the out-y signal means for y-aXis sweep signals; a plurality of diodes each having -a cathode and an anode; means to' couple said anodes to said first and second input `signal means; means to connect said cathodes to a common point; a first triode having a grid, a cathode, and an anode; means to couple the `grid of said first triode to said common point; a second triode having a cathode, a grid and an anode; means to Iconnect the anode of said first triode to the grid Vof said secondtriode; a relay coupled to the anode of said second triode; lblanliing means coupled to said relay; afirst and a second capacitor coupled to said first and second input signal means, respectively; a first and second diode connected to said first capacitor; a third and fourth diode connected to said second capacitor; means to connect said third diode tosaid firstdiode; means to connect said fourth diodeto said second diode; a first source of negative potential coupled to saidfirst and third diodes; a fifth diode having its cath-ode connected to said second and lfourth diodes and itsanode coupled to the grid of said first triode; and a second source of negative potential coupled to said second, fourth and fifth diodes.

12. A sweep collapse alarm system as described in claim 11 including means coupled to the grid of said first Y triode .to test the operation of `said alarm system.

1'3. A sweep collapse alarmsystem as described in claim 11 including a plurality of cathode-ray tubes cou-g' pled to said blanlting circuits.

y References Cited hy the Errarnimer;Y UNITED STATES PATENTS DAViD RBDIRNBTAUGI-I, Primary Examiner. p ARTHUR GAUSS, ROBERT SEGAL, Examiners. 

1. IN A PPI RADAR SYSTEM, A SWEEP COLLAPSE ALARM SYSTEM COMPRISING: A ROTATION MONITOR; AN R.M.S. COMPUTER; MEANS TO APPLY TWO INPUT SIGNALS TO BOTH SAID MONITOR AND SAID COMPUTER, AN AMPLIFIER COUPLED TO SAID MONITOR AND SAID COMPUTER; A RELAY DRIVER COUPLED TO SAID AMPLIFIER; AND A RELAY COUPLED TO SAID DRIVER. 